The present invention relates in general to a fuel injection pump for an internal combustion engine and in particular to a pump of the type having at least one pumping piston delimiting a variable work space, a fuel injection conduit, distributing means for connecting the work space during each delivery stroke to the fuel injection conduit and, during each suction stroke, to a fuel storage space and having a relieving opening for connecting, at a certain point during the delivery stroke of the pumping piston, the work space of the pump to a fuel offtake space.
A fuel injection pump of this kind is known from the U.S. Pat. No. 3,988,287. This prior art pump is constructed as a reciprocating distributor type injection pump provided with a relieving channel which is arranged in the pump piston and branches from the work space of the pump. The relieving channel has a lateral outlet on the pumping piston and at a certain stroke piston of the latter communicates during each delivery stroke with a relieving conduit which in turn is connected via a variable and a fixed throttle with a relieving space of a constant volume. The reception capacity of this volume in this known fuel injection pump is set on the one hand, by the variable throttle which is adjustable in dependency on load and on the other hand, by the fixed throttle which acts on dependency on rotary speed. By means of this arrangement, a connection between the pumping work space and the fuel offtake space is to be established only during low rotary speeds and loads and the quantity of fuel per an angle of rotation or per a time unit is reduced at the beginning of injection, particularly during low rotary speeds and loads. This prior art arrangement of injection pump does not permit any universal application thereof. Also it cannot adjust for the overall operational range of the combustion engine the amount of a preliminary fuel injection before the actual main fuel injection and the time interval between the preliminary and main injections.